Previous studies on the serine/threonine protein phosphatase (PP-1) activity in skeletal muscle indicated increased amounts of activity in insulin-sensitive individuals, but increased protein amounts in insulin- resistant persons. Subsequently, studies on the steady state RNA levels of PP-1 alpha in human skeletal muscle revealed no differences between insulin-sensitive and resistant persons. In addition, a second isoform of PP-1 was cloned, suggesting that PP-1 activity may be a composite of several protein isoforms. Since the observed activity and protein differences are not accounted for by differences in the amount of RNA in these two groups, mutations in the coding regions of either of the two skeletal muscle PP-1 isoforms could explain the activity and proteins differences. Currently, the genes for both of the skeletal muscle protein phosphatase isoforms are being isolated. The genomic clones for both of these genes will be analyzed and suitable PCR primer pairs chosen from the non-coding regions that will allow amplification of PP-1 coding regions. The coding regions of both these genes will be examined in insulin- sensitive and -resistant persons for single stranded conformational polymorphisms (SSCP). SSCPs that result in amino acid changes will be further tested for a relationship to insulin resistance and type II diabetes.